The invention relates to a semiconductor device comprising two P,N.sup.-, N- or N, P.sup.-, P-diodes arranged in series and in opposition and having a semiconductor body with two relatively low-ohmic surface zones of one conductivity type which adjoin a substantially flat surface of the body and which extend in a relatively high-ohmic semiconductor surface layer which is common to the diodes, the high-ohmic layer extending from the surface farther into the semiconductor body than the surface zones and separating them from a low-ohmic region of the opposite conductively type, the low-ohmic region and the two surface zones being provided with an electrically conductive connection contact.
Such semiconductor devices are known, for example, from Electronics, Apr. 29, 1968, pp 75-79. In particular page 76 shows a number of embodiments of combinations of two P, N.sup.-, N- or N, P.sup.-, P-diodes hereinafter briefly referred to as PIN-diodes.
Many application possibilities exist for combinations of two PIN-diodes arranged in series and in opposition and they are in particular important also for circuits for high frequencies in the range of, for example, 10 MHz to 10 GHz and higher. They may be used as switches or controllable capacitors or, for example, in (electronically controllable) attenuators, phase shifting networks or modulators. These functions play an important part inter alia in electronic data methods, such as f.m. radio, television and radar.
As is known, the high frequency signal during operation is usually supplied to one of the two contacted surface zones, the other contacted surface zone forming the high frequency signal output. By means of the contacted low-ohmic region which is provided on the oppositely located side of the semiconductor body and which forms the center contact of the combination connected to the mode point of the two diodes, the two diodes are biased usually in the forward direction and sometimes in the reverse direction. In switches and attenuators, said bias may be obtained by means of direct current, while for this purpose, for example in modulators or ring-mixers, a low frequency alternating current signal in combination with a direct current is used. The fact is used that the differential resistance of the diodes is current-dependent in so far as direct current and comparatively slow current variations are concerned, but is substantially not influenced by or is at least much less sensitive to high frequency current variations.
The known diode combinations suffer from drawbacks notably from a point of view of manufacture. In connection with the required low series resistance in the forward direction, the surface zones on the one hand and the low-ohmic region on the other hand are present on oppositely located sides of the common high-ohmic semiconductor layer, as a result of which the semiconductor body has to be contacted on two sides. As a result of this, said devices are not suitable for use of direct contact methods in assembling. They cannot be provided with usual "beam leads" either, although as is known, connections in beam-lead form are advantageous at high frequencies due to their low inductance. Moreover, said devices are less suitable for use in integrated circuits. As a matter of fact, integration of high frequency circuits is attractive in particular if the electric connections between the circuit elements can be obtained in a simple manner and are relatively short so that the parasitic effects associated with said connections are considerably reduced. The said advantage can be realized to a restricted extent only with the known diode combinations.
By using the invention, the above-mentioned and other drawbacks can be mitigated entirely or at least partly.